This invention relates to a process of preparing m-chlorobenzotrifluoride by reaction between benzotrifluoride and chlorine in the presence of a catalyst.
In the chemical industry m-chlorobenzotrifluoride is a compound useful as an intermediate in the preparation of various organic substances including dyes, pigments, medicines and agricultural chemicals.
As is known, m-chlorobenzotrifluoride can be prepared by making chlorine react with benzotrifluoride in the presence of a catalyst to accomplish chlorine substitutation in the benzene nucleus. However, by this reaction it is impossible to convert benzotrifluoride exclusively to m-chlorobenzotrifluoride. The reaction product always contains considerable amounts of isomers, i.e. o- and p-chlorobenzotrifluorides, and dichlorobenzotrifluoride isomers. The isolation of m-chlorobenzotrifluoride formed by the reaction is difficult especially because of the small difference between the boiling point of m-chlorobenzotrifluoride (138.1.degree. C.) and the boiling point of p-chlorobenzotrifluoride (139.2.degree. C.). Therefore, there is a strong demand for a new technique to carry out monochlorination of benzotrifluoride with chlorine gas with high selectivity for m-chlorobenzotrifluoride and also with high ratio of m-chlorobenzotrifluoride to p-chlorobenzotrifluoride in the reaction product.
With respect to the above described reaction, U.S. Pat. No. 3,234,292 proposes to use a combination of ferric chloride and either sulfur chloride or sulfur dichloride as the catalyst. By this method, however, the selectivity for m-chlorobenzotrifluoride is too low and the ratio of the m-substitute to the p-isomer is also low. Besides, this method requires a long time to complete the reaction because of relatively low activity of the catalyst and suffers from low conversion efficiency of chlorine and, hence, can hardly be taken as suited to industrial practice.